Ultra-small LED electrode assembly having improved luminance and method of manufacturing the same

ABSTRACT

An ultra-small light-emitting diode (LED) electrode assembly having an improved luminance is provided. More particularly, an ultra-small LED electrode assembly in which light, which is blocked by an electrode and cannot be extracted, is minimized, an ultra-small LED device is connected to an ultra-small electrode without a defect such as an electrical short-circuit, and a very excellent luminance is exhibited even at a direct current (DC) driving voltage, and a method of manufacturing the same are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/705,284, filed on Sep. 15, 2017, the entire content of which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an ultra-small light-emitting diode(LED) electrode assembly, and more particularly, to an ultra-small LEDelectrode assembly in which light, which is blocked by an electrode andcannot be extracted, is minimized, an ultra-small LED device isconnected to an ultra-small electrode without a defect such as anelectrical short-circuit, and a very excellent luminance is exhibitedeven at a direct current (DC) driving voltage, and a method ofmanufacturing the same.

BACKGROUND

Light-emitting diode (LED) devices have been actively developed sinceNakamura and the like of Nichia Corporation of Japan succeeded in fusinga high-quality monocrystalline GaN nitride semiconductor in 1992 byapplying a low-temperature GaN compound buffer layer thereto. An LED isa semiconductor having a structure in which an N-type semiconductorcrystal in which a plurality of carriers are electrons and a P-typesemiconductor crystal in which a plurality of carriers are holes arebonded to each other by using a characteristic of a compoundsemiconductor, and is a semiconductor device which converts anelectrical signal into light having a wavelength band of a desiredregion to display the light. In Korea Unexamined Patent ApplicationPublication No. 2009-0121743, a method of manufacturing an LED and anLED manufactured thereby are disclosed.

The LED is a green component which has very low energy consumption dueto high light conversion efficiency, has a semi-permanent lifetime, andis environmentally friendly. LEDs are being applied in many fields suchas traffic lights, mobile phones, automobile headlights, outdoorelectric signboards, liquid-crystal display (LCD) backlight units(BLUs), indoor/outdoor lights, and the like, and are being activelyresearched domestically and internationally.

As part of the above research, research on an ultra-small LED devicewhich is manufactured to have a nano size or a micro size is activelybeing conducted, and research for utilizing such an ultra-small LEDdevice in lighting, a display, and the like is being continued. In suchresearch, an electrode for applying power to an ultra-small LED device,an electrode arrangement for reducing a space occupied by the electrodeand an application purpose, a method of mounting an ultra-small LED onan arranged electrode, and the like are continuously being focused on.

Among the above things, the method of mounting an ultra-small LED on anarranged electrode still has difficulty in that it is very difficult toarrange and mount an ultra-small LED device on a target electrode due toa size limitation of the ultra-small LED device. This is because theultra-small LED device is on a nano-scale or micro-scale and may not bearranged and mounted in a target electrode region by a human hand.

Also, even when the ultra-small LED device is mounted in the targetelectrode region, it is very difficult to adjust the number ofultra-small LED devices included in a unit electrode region and apositional relationship between ultra-small LED devices and electrodesas desired. When LED devices are arranged on a two-dimensional plane,the number of LED devices included in a unit area is limited and it isdifficult to obtain an excellent amount of light. Furthermore, becauseall ultra-small LED devices connected to two different electrodes cannotemit light without a defect such as an electrical short-circuit and thelike, it is more difficult to obtain a desired amount of light.

Accordingly, the inventor of the present invention has proposed a methodof manufacturing a nano-scaled ultra-small LED device which isimplemented as an electrode assembly by applying power to theultra-small electrode line in Korean Patent Registration No. 10-1490758to implement an ultra-small LED electrode assembly. However, in theultra-small LED electrode assembly implemented by such a technique, thenumber of ultra-small LED devices which do not emit light when a DC isapplied thereto as driving power is significantly increased, and thus itis difficult to obtain a desired luminance. In order to address theabove problem, there is a selection limitation of power to which analternating current (AC) should be applied as the driving power. Suchresults are due to characteristics of the LED itself as a rectifier. Adirection of a current in a device may be determined by a structure oflayers in the device. For example, in the case of an LED in which aP-type semiconductor and an N-type semiconductor are bonded to eachother, when positive (+) power is connected to the P-type semiconductorand negative (−) power is connected to the N-type semiconductor, acurrent may flow through the LED due to a potential difference generatedwhile free electrons of the N-type semiconductor move toward positiveholes of the P-type semiconductor, and the LED may emit light while thefree electrons recombine with the positive holes. However, since nocurrent flows in the LED when the negative (−) power is connected to theP-type semiconductor and the positive (+) power is connected to theN-type semiconductor, an ultra-small LED electrode assembly implementedto have no semiconductor directionality of ultra-small LED devices andno disposition tendency between different mounting electrodes has aproblem in that some of the ultra-small LED devices may not emit lightwhen DC driving power is applied thereto and a luminance thereof issignificantly reduced.

Accordingly, research on an ultra-small LED electrode assembly in whichultra-small LED devices communicate without an electrical short-circuit,a selection limitation of driving power is removed, and a luminancethereof is further improved is urgently required.

SUMMARY OF THE INVENTION

The present invention is directed to an ultra-small light-emitting diode(LED) electrode assembly in which light, which is blocked by anelectrode and cannot be extracted, is minimized and an ultra-small LEDdevice is connected to an ultra-small electrode without a defect such asan electrical short-circuit, and a method of manufacturing the same.

The present invention is directed to an ultra-small LED electrodeassembly in which a selection limitation of driving power of theultra-small LED electrode assembly is removed and a luminancecharacteristic is sufficiently exhibited even through direct current(DC) driving power, and a method of manufacturing the same.

The present invention is directed to an ultra-small LED electrodeassembly in which a luminance characteristic is sufficiently exhibitedthrough DC driving power and is more improved than that of aconventional ultra-small LED electrode assembly, and a method ofmanufacturing the same.

The present invention is directed to a backlight unit (BLU) in which anexcellent luminance characteristic can be exhibited through theultra-small LED electrode assembly according to the present invention,and a display including the same.

The present invention is directed to a lamp in which an excellentluminance characteristic can be exhibited, and an intensity of light fora desired specific color is improved through the ultra-small LEDelectrode assembly according to the present invention.

According to an aspect of the present invention, there is provided amethod of manufacturing an ultra-small LED electrode assembly having animproved luminance including (1) a step of introducing a solutionincluding a plurality of ultra-small LED devices to an electrode lineincluding a first mounting electrode and a second mounting electrodewhich is formed on the same plane as the first mounting electrode to bespaced apart from the first mounting electrode and (2) a step ofapplying power having an asymmetric assembly voltage of 10 V or moreaccording to the following Equation 1 to the electrode line andself-mounting the plurality of ultra-small LED devices such that ends ofeach of the ultra-small LED devices come into contact with the firstmounting electrode and the second mounting electrode,Asymmetric assembly voltage(V)=|A(V)|−|B(V)|  [Equation 1]

wherein A and B denote magnitudes of an upper peak voltage of appliedpower and a lower peak voltage of the applied power, respectively.

The power may have a frequency of 50 kHz to 1 GHz.

The power may have an asymmetric assembly voltage of 18 V or moreaccording to the above Equation 1.

The power may have an effective voltage (V_(rms)) of 12 V or more.

The method may further include (3) a step of performing heat treatmentat a temperature of 200 to 1,000° C. for 0.5 to 10 minutes on theelectrode line and the ultra-small LED devices self-mounted on theelectrode line after performing the step (2).

The method may further include a step of forming an ohmic layer at theends of each of the ultra-small LED devices which come into contact withthe first mounting electrode and the second mounting electrode afterperforming the step (2).

The power may have an asymmetric assembly voltage of 25 V or moreaccording to the above Equation 1.

According to another aspect of the present invention, there is providedan ultra-small LED electrode assembly having an improved luminanceincluding an electrode line including a first mounting electrode and asecond mounting electrode which are formed on the same plane and spacedapart from each other, and a plurality of ultra-small LED devices eachhaving one end in contact with the first mounting electrode and theother end in contact with the second mounting electrode, wherein aluminance gain according to the following Equation 2 is 1.1 or more,

$\begin{matrix}{{{Luminance}\mspace{14mu}{gain}} = \frac{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{DC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{3}} \right)}\end{matrix}\mspace{14mu}}{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{AC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{3}} \right)}\end{matrix}\mspace{14mu}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

wherein a magnitude of the applied DC voltage (V) is the same as aneffective voltage (V_(rms)) of AC power having a sine waveform.

An aspect ratio of the ultra-small LED devices may range from 1.2 to100. The ultra-small LED devices each may have a length 100 nm to 10 μm.

Each of the ultra-small LED devices may include a first conductivesemiconductor layer, an active layer formed on the first conductivesemiconductor layer, a second conductive semiconductor layer formed onthe active layer, and an insulating film configured to cover at least anentire outer surface of an active layer portion of outer surfaces of thedevices. In this case, any one of the first conductive semiconductorlayer and the second conductive semiconductor layer may include at leastone N-type semiconductor layer and the other conductive semiconductorlayer may include at least one P-type semiconductor layer.

The ultra-small LED electrode assembly may have a luminance gain of 1.3or more according to the above Equation 2.

The ultra-small LED electrode assembly may include 1,000 or moreultra-small LED devices mounted per unit area (mm²).

The ultra-small LED electrode assembly may further include an insulatingfilm formed on outer surfaces of the first mounting electrode and thesecond mounting electrode and the plurality of ultra-small LED devicesmay come into contact with the first mounting electrode and the secondmounting electrode through the insulating film.

According to still another aspect of the present invention, there isprovided an ultra-small LED electrode assembly having an improvedluminance including an electrode line including a first mountingelectrode and a second mounting electrode which are formed on the sameplane and spaced apart from each other, and a plurality of ultra-smallLED devices each including a first semiconductor and a secondsemiconductor, and each having one end in contact with the firstmounting electrode and the other end in contact with the second mountingelectrode, wherein the number of the ultra-small LED devices in whichthe first semiconductor comes into contact with the first mountingelectrode is 60% or more of the total number of the ultra-small LEDdevices.

The number of the ultra-small LED devices in which the firstsemiconductor comes into contact with the first mounting electrode maybe 80% or more of the total number of the ultra-small LED devices.

The ultra-small LED electrode assembly may further include an insulatingfilm formed on outer surfaces of the first mounting electrode and thesecond mounting electrode and the plurality of ultra-small LED devicesmay come into contact with the first mounting electrode and the secondmounting electrode through the insulating film.

According to yet another aspect of the present invention, there isprovided a BLU unit including the ultra-small LED electrode assemblyaccording to the present invention.

According to yet another aspect of the present invention, there isprovided a lamp including the ultra-small LED electrode assemblyaccording to the present invention.

Hereinafter, terms used in the present invention will be described.

In embodiments according to the present invention, a “mountingelectrode” refers to an electrode which comes into direct contact witheach of both ends of an ultra-small LED device. A power source may bedirectly connected to the mounting electrode to drive an ultra-small LEDelectrode assembly, and an address electrode or a gate electrode whichapplies power to the mounting electrode may be further provided.

In the embodiments according to the present invention, when a layer, aregion, a pattern, or a structure is described as being formed “on,” “onan upper portion of,” “above,” “under,” “on a lower portion of,” or“below” a substrate, the description of the layer, the region, thepattern, or the structure includes the meaning of “directly formed” and“indirectly formed.”

In the embodiments according to the present invention, when a “firstcomponent” is described as coming into contact with a “secondcomponent,” the description includes the meaning of the first componentand the second component coming into direct contact with each other orbeing indirectly structurally connected through a third component. Forexample, the phrase “a first conductive semiconductor coming intocontact with a first mounting electrode” includes the meaning of thefirst mounting electrode being directly structurally connected to thefirst conductive semiconductor and the meaning of an electrode layerbeing formed on the first conductive semiconductor, the electrode layerand the first mounting electrode being structurally connected to eachother, and the first mounting electrode being indirectly connected tothe first conductive semiconductor. Meanwhile, the structural connectiondoes not refer to an electrical connection related to whether anultra-small LED device emits light when driving power is applied to anelectrode line, and includes all physical contact even when theelectrical connection is not established.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent to those of ordinary skill in theart by describing exemplary embodiments thereof in detail with referenceto the accompanying drawings, in which:

FIGS. 1A to 1C are views of an ultra-small light-emitting diode (LED)electrode assembly according to one embodiment of the present invention,wherein FIG. 1A is a perspective view of the ultra-small LED electrodeassembly, FIG. 1B is a luminescent photograph when alternating current(AC) power is applied to the ultra-small LED electrode assembly asdriving power, and FIG. 1C is a luminescent photograph when directcurrent (DC) power is applied to the ultra-small LED electrode assemblyas driving power;

FIGS. 2A to 2C are views of an ultra-small LED electrode assemblymanufactured by a conventional method, wherein FIG. 2A is a perspectiveview of the ultra-small LED electrode assembly, FIG. 2B is a luminescentphotograph when AC power is applied to the ultra-small LED electrodeassembly as driving power, and FIG. 2C is a luminescent photograph whenDC power is applied to the ultra-small LED electrode assembly as drivingpower;

FIG. 3 shows schematic views illustrating a process of manufacturing anultra-small LED electrode assembly according to one embodiment of thepresent invention;

FIGS. 4A to 4C are schematic views illustrating electrostatic attractionbetween an ultra-small LED device and a mounting electrode under anelectric field, wherein FIG. 4A is a schematic view illustrating thecase before power is applied to the mounting electrode, FIG. 4B is aschematic view illustrating the case in which symmetrical assembly poweris applied to the mounting electrode, and FIG. 4C is a schematic viewillustrating the case in which asymmetrical assembly power is applied tothe mounting electrode;

FIG. 5 is a schematic view illustrating various types of contact betweenmounting electrodes and both ends of an ultra-small LED device in anultra-small LED electrode assembly according to one embodiment of thepresent invention;

FIG. 6 is an exploded perspective view illustrating a light-receivingdisplay including a backlight unit (BLU) having a light source whichincludes an ultra-small LED electrode assembly according to oneembodiment of the present invention;

FIGS. 7A and 7B are views of an ultra-small LED electrode assemblyaccording to one embodiment of the present invention, wherein FIG. 7A isa luminescent photograph when AC power is applied to the ultra-small LEDelectrode assembly as driving power and FIG. 7B is a luminescentphotograph when DC power is applied to the ultra-small LED electrodeassembly as driving power; and

FIG. 8 is a graph illustrating assembly power applied when anultra-small LED electrode assembly according to one embodiment of thepresent invention is implemented.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention that are easilyperformed by those skilled in the art will be described in detail withreference to the accompanying drawings. The present invention may beimplemented in several different forms and is not limited to theembodiments described herein. Parts irrelevant to description areomitted in the drawings in order to clearly explain the presentinvention. The same or similar components are denoted by the samereference numerals throughout this specification.

As illustrated in FIG. 1A, an ultra-small light-emitting diode (LED)electrode assembly according to the present invention includes anelectrode line including a first mounting electrode 110 and a secondmounting electrode 130 which are spaced apart from each other on thesame plane and a plurality of ultra-small LED devices 121 and 122 eachhaving one end in contact with the first mounting electrode and theother end in contact with the second mounting electrode.

In the ultra-small LED electrode assembly illustrated in FIG. 1A, thefirst mounting electrode 110 and the second mounting electrode 130 arelocated on the same plane, and thus the ultra-small LED devices 121 and122 may be connected to the electrodes by being laid down. Therefore,there is an advantage in that the number of devices electricallyconnected to the electrodes is increased because it is not necessary fornano-scaled ultra-small LED devices to be three-dimensionally uprightand to be bonded to the electrodes. In addition, photons generatedinside the ultra-small LED devices are blocked by the electrodes andcannot be extracted and extinction of the photons therein is minimized,and thus light extraction efficiency of the ultra-small LED device canbe significantly improved.

Meanwhile, in the ultra-small LED electrode assembly illustrated in FIG.1A, all of a width of each of the electrodes, a distance between theelectrodes, and a size of each of the ultra-small LED devices are on amicro-scale or nano-scale, and thus it is almost impossible for a personor a machine to mount and manufacture the individually separatedultra-small LED devices one by one. Accordingly, the inventor of thepresent invention has manufactured an ultra-small LED electrode assemblyillustrated in FIG. 2A using a method in which a solution includingultra-small LED devices is dropped onto an ultra-small electrode line,assembly power is applied to the ultra-small electrode line, and theultra-small LED devices are then self-aligned with and connected to twodifferent mounting electrodes. The inventor has confirmed that when theultra-small LED electrode assembly is actually driven with drivingpower, which is alternating current (AC) power, the ultra-small LEDelectrode assembly emits light (see FIG. 2B).

However, the ultra-small LED electrode assembly illustrated in FIG. 2Ahas a problem in that the number of devices that actually emit lightwhen direct current (DC) power is used as driving power instead of ACpower is significantly reduced. Specifically, when a degree of emissionof visual light of an ultra-small LED electrode assembly that emitslight by being driven according to a DC voltage, as illustrated in FIG.2C, and a degree emission of visual light of an ultra-small LEDelectrode assembly that emits light by being driven according to an ACvoltage, as illustrated in FIG. 2B, are compared to each other byvarying only the type of driving power for the same ultra-small LEDelectrode assembly, it can be confirmed that light emitting efficiencyis significantly reduced when DC power is used as the driving power.

As illustrated in FIG. 2C, the problem of the luminance being reducedwhen the DC driving power is applied is because there is no alignmenttendency between different mounting electrodes which come into direct orindirect contact with different conductive semiconductors (e.g., aP-type semiconductor and an N-type semiconductor) in each of theultra-small LED devices in the electrode assembly. Specifically, asillustrated in FIG. 2A, in four of eight ultra-small LED devices mountedon the ultra-small LED electrode assembly, the same type ofsemiconductor comes into contact with the first mounting electrode 10,like in a first ultra-small LED device 21. In the other four ultra-smallLED devices, the other type of semiconductor device comes into contactwith the first mounting electrode 10. Therefore, when one-way DC drivingpower is applied to the ultra-small LED electrode assembly illustratedin FIG. 2A, only four of the ultra-small LED devices can emit light andthe remaining four ultra-small LED devices cannot emit light. Thisproblem is directly related to luminance reduction.

As a result, when the ultra-small LED devices are self-aligned by aconventional manufacturing method, both ends of each of the ultra-smallLED device may come into contact with two different electrodes,respectively. However, in the manufactured ultra-small LED electrodeassembly, each of the ultra-small LED devices in contact with the firstmounting electrode has a specific one end, for example, a P-typesemiconductor, which comes into contact with only the first mountingelectrode, and some of the ultra-small LED devices have an N-typesemiconductor, which comes into contact with the first mountingelectrode. Since a semiconductor layer which also comes into contactwith a specific mounting electrode is different every time theultra-small LED electrode assembly is manufactured, an ultra-small LEDelectrode assembly which can emit light by using a DC voltage as drivingpower can be manufactured in some cases, but such an electrode assemblycannot always be manufactured.

As a result of continuing research to address the problem of a selectionlimitation of the driving power of the conventional ultra-small LEDdevice described above by the inventor of the present invention, whenthe ultra-small LED device is self-aligned by applying assembly power tothe ultra-small LED electrode assembly under a specific condition of thepresent invention, a specific semiconductor layer in the ultra-small LEDdevice may come into contact with a specific mounting electrode, andspecifically, a first conductive semiconductor layer or a secondconductive semiconductor layer may be self-aligned with a first mountingelectrode or a second mounting electrode. Therefore, it can be confirmedthat the ultra-small LED electrode assembly may be driven through DCdriving power, and, at the same time, a more improved luminancecharacteristic may be exhibited, which leads to the present invention.

Hereinafter, first, a method of manufacturing an ultra-small LEDelectrode assembly according to the present invention that may be drivenby a DC voltage, as described above, will be described.

The method of manufacturing the ultra-small LED electrode assemblyaccording to the present invention includes (1) a step of introducing asolution including a plurality of ultra-small LED devices to anelectrode line including a first mounting electrode and a secondmounting electrode, which is formed on the same plane as the firstmounting electrode to be spaced apart from the first mounting electrode,and (2) a step of applying power, which has an asymmetric assemblyvoltage of 10 V or more according to the following Equation 1, to theelectrode line and self-mounting the plurality of ultra-small LEDdevices such that ends of each of the ultra-small LED devices come intocontact with the first mounting electrode and the second mountingelectrode.

First, in step (1), the introducing of the solution including theplurality of ultra-small LED devices into the electrode line includingthe first mounting electrode and the second mounting electrode, which isformed on the same plane as the first mounting electrode to be spacedapart from the first mounting electrode, is performed.

Specifically, FIG. 3 shows schematic views illustrating a process ofmanufacturing an ultra-small LED electrode assembly according to oneembodiment of the present invention. In FIG. 3(a), the first mountingelectrode 110 formed on a base substrate 100, the second mountingelectrode 130 which is formed on the same plane as the first mountingelectrode to be spaced apart from the first mounting electrode, and asolution (ultra-small LED devices 120 and a solvent 140) including aplurality of ultra-small LED devices are illustrated. Although notillustrated in FIG. 3, an insulating partition may be further providedin a mountable region of the electrode line to which the solutionincluding the ultra-small LED devices is introduced to prevent thesolution from spreading beyond a region of the electrode line in whichthe ultra-small LED devices will be mounted after the solution includingthe ultra-small LED devices is introduced thereto.

Since a specific method of manufacturing the base substrate, theelectrode line including the first mounting electrode and the secondmounting electrode, and the insulating partition that can be formed onthe electrode line, a structure, a solvent in the introduced solution,the content of the ultra-small LED devices in the solution, and the likemay be described with reference to Korean Patent Registration No.10-1429095 and Korean Patent Application No. 10-2014-0085384 by theinventors of the present invention, detailed descriptions thereof willbe omitted in the present invention.

According to one embodiment of the present invention, an insulating filmmay be further provided on outer surfaces of the first mountingelectrode and the second mounting electrode. Due to a distance betweenthe first mounting electrode and the second mounting electrode reduceddue to the insulating film, the ultra-small LED device may beself-mounted so that all of both ends thereof are located on the firstmounting electrode and the second mounting electrode. In this case, thenumber of ultra-small LED devices that can be mounted may be increaseddue to improvement of mounting alignment of the ultra-small LED devices,and a more highly-efficient ultra-small LED electrode assembly may beeasily implemented. Further, in step (2) described below, theultra-small LED devices may be introduced into the first mountingelectrode and the second mounting electrode in a mixed state with thesolvent. When power is applied to the ultra-small LED devices in orderto self-mount thereof, electrical short-circuit may occur between twodifferent mounting electrodes due to the solvent, and thus theelectrodes may be damaged. However, there is an advantage in thatelectrical short-circuit between the electrodes due to the solvent maybe prevented by the insulating film provided on the outer surfaces ofthe first mounting electrode and the second mounting electrode.

Next, in step (2) according to the present invention, the applying ofthe power, which has an asymmetric assembly voltage of 10 V or moreaccording to the following Equation 1, to the electrode line and theself-mounting of the plurality of ultra-small LED devices such that theends of each of the ultra-small LED devices come into contact with thefirst mounting electrode and the second mounting electrode areperformed.

In step (2), an electric field is formed on the mounting electrode,polarization occurs in the ultra-small LED device under the electricfield, and the device may be moved to, self-aligned with, and mounted onthe electrode by itself through various physical forces such as anelectrostatic attraction between the polarized ultra-small LED deviceand an mounting electrode adjacent thereto and the like. However, inorder to improve an orientation of the mounted ultra-small LED devicesso that each of the devices is moved to and self-aligned with theelectrode by itself and the first conductive semiconductor layer in thedevice comes into contact with the first mounting electrode, it isnecessary to apply the power, which has an asymmetric assembly voltageof 10 V or more according to the following Equation 1, to the electrodeline.Asymmetric assembly voltage (V)=|A(V)|−|B|(V)  [Equation 1]

wherein A and B denote magnitudes of an upper peak voltage and a lowerpeak voltage of the applied power, respectively.

In the conventional ultra-small LED electrode assembly by the presentinventor, a symmetrical assembly voltage with a value according to theabove Equation 1 of 0 V is used as the power applied in step (2). Such asymmetrical assembly voltage randomly determines an orientation of aspecific mounting electrode of the ultra-small LED device, and thus theultra-small LED device may not be mounted to have a specificorientation.

Specifically, FIG. 4A corresponds to a state immediately after step (1)and illustrates an ultra-small LED device 120 including a firstconductive semiconductor layer 120 b and a second conductivesemiconductor layer 120 d which are introduced into a different firstmounting electrode 110 and second mounting electrode 130. Although notillustrated in FIG. 4A, the ultra-small LED devices 120 is mixed with asolvent. Conventionally, as illustrated in FIG. 4B, voltages are appliedso that magnitudes of peaks of the voltages applied to the firstmounting electrode 110 and the second mounting electrode 130 aresymmetrical (V_(AC)=±30 V). In this case, as illustrated in FIG. 2B,when lengths of the first conductive semiconductor layer 120 b and thesecond conductive semiconductor layer 120 d in the ultra-small LEDdevice are the same and all other influences of the surroundings areexcluded, magnitudes a1 and a2 of electrostatic attractions applied tothe ultra-small LED device between two electrodes may be the same. Inthis case, a probability that the first conductive semiconductor layer120 b comes into contact with the first mounting electrode 110 may be50%. Expanding on this, in each of the plurality of ultra-small LEDdevices introduced to the mounting electrodes, the first conductivesemiconductor layer 120 b may come into contact with the first mountingelectrode 110 at a probability of about 50% and a probability that atotal of ten ultra-small LED devices are mounted to and come intocontact with the first mounting electrode 110 is only (½)¹⁰.

However, as illustrated in FIG. 4C, when voltages are asymmetricallyapplied to the first mounting electrode 110 and the second mountingelectrode 130, since a polarization state on a surface of theultra-small LED device is formed different from that of FIG. 4B,electrostatic attractions b1 and b2 for moving the first conductivesemiconductor layer 120 b toward the first mounting electrode 110 andmoving the second conductive semiconductor layer 120 d toward the secondmounting electrode 130 become stronger, and a probability that the firstconductive semiconductor layer 120 b comes into contact with the firstmounting electrode 110 is significantly increased. Expanding on this,the plurality of the ultra-small LED devices introduced to the mountingelectrode may have an orientation and may more easily come into contactwith the first mounting electrode.

However, immediately after step (1) is performed, all of the ultra-smallLED devices may not be arranged in parallel between the two electrodes,as illustrated in FIG. 4A. Some of the ultra-small LED devices may beobliquely arranged at varying degrees and the other ultra-small LEDdevices may be placed on any one of the mounting electrodes. Theultra-small LED devices may be asymmetrically formed so that lengths ofthe conductive semiconductor layers in the ultra-small LED devices aredifferent. Therefore, in order to further improve an orientation of aspecific semiconductor layer of the ultra-small LED device to come intocontact with a specific mounting electrode in consideration of all ofthese situations, an asymmetric assembly voltage of the assembly powerapplied to the mounting electrodes must be 10 V or more, preferably, 14V, more preferably, 18 V, and most preferably, 25 V or more, accordingto the above Equation 1. When the asymmetric assembly voltage accordingto Equation 1 is less than 10 V, the orientation is reduced such thatthe specific semiconductor layer of the ultra-small LED device comesinto contact with the specific mounting electrode. Therefore, there is aproblem in that the luminance when a DC is applied to the manufacturedultra-small LED electrode assembly as driving power is significantlylowered in comparison to when an AC is applied thereto as the drivingpower. On the other hand, when the asymmetric assembly voltage accordingto Equation 1 is more than 50 V, there is no problem of the orientationof the ultra-small LED device being in a specific direction, but theelectrode may be damaged.

Meanwhile, A and B in the above Equation 1 do not refer to voltagesrespectively applied to the first mounting electrode and the secondmounting electrode. That is, when 30 V, 0 V, 30 V, 0V, . . . are appliedto the first mounting electrode at a predetermined cycle and 0 V, 30 V,0 V, 30 V, . . . are applied to the second mounting electrode at thesame cycle, such a power application method is the same as when +30 Vand −30 V are applied to the mounting electrode line with a pulse waveat a predetermined cycle. In this case, the value according to the aboveEquation 1 is zero, which means that a symmetrical voltage is applied tothe electrodes.

According to one embodiment of the present invention, the power may bepower having a predetermined cycle, preferably, power having a frequencyof 50 kHz to 1 GHz, and more preferably, power having a sine wavewaveform having a frequency of 90 kHZ to 100 MHz.

When the power is power having no cycle, for example, when apredetermined voltage is continuously applied to the mounting electrodeswithout change, the mounting electrodes may be damaged even when theabove-described Equation 1 is satisfied. When there is much damage, themounted ultra-small LED device may not be driven by the mountingelectrode.

In the case in which the frequency is less than 50 kHz, even when avoltage range is satisfied, the number of the mounted ultra-small LEDdevices is significantly reduced, the device orientation also becomesvery irregular, and thus a DC may not be used as the driving power. Inthe case in which the frequency is more than 1 GHz, since theultra-small LED device may not adapt to rapidly changing power, amounting property of the device is lowered, the orientation thereof isalso reduced, and as a result, a DC may not be used as the driving powerlike in the case of the low frequency.

Meanwhile, preferably, the above-described power may have an effectivevoltage V_(rms) of 12 V or more, and more preferably, of 17 V or more.This is because the number of ultra-small LED devices mounted when aneffective voltage of power is low may be reduced. That is, when thepower satisfies the value according to the above-described Equation 1and is applied to the mounting electrodes to implement the ultra-smallLED electrode assembly, DC driving may be possible because a mountingtendency in which a specific semiconductor layer of the ultra-small LEDdevice is electrically connected to a specific mounting electrode ishigh. However, the number of the mounted ultra-small LED devices isreduced, and thus there is a concern that an amount of light emittedwhen the driving power is applied is significantly lowered.

After performing step (2), (3) a step of performing heat treatment at atemperature of 300 to 1000° C. for 0.5 to 10 minutes may be furtherperformed on the electrode line and the ultra-small LED devicesself-aligned on the electrode line. In this case, the heat treatmenttemperature may be more preferably 600° C. or more. The heat treatmentstep is a process for causing the ultra-small LED devices to come intocontact with different mounting electrodes and then removing the solventthat was introduced to facilitate movement and alignment of theultra-small LED devices. When the driving power is applied in a state inwhich the solvent is not completely removed or a metal ohmic layer isformed to reduce a contact resistance between the mounting electrode andthe ultra-small LED device, the ultra-small LED electrode assembly mayfail to exhibit a desired level of light emitting efficiency. Also,unremoved solvent may cause process defects in a step of forming themetal ohmic layer, a degree of formation thereof may be slight even whenthe metal ohmic layer is formed, and a large current loss may occur.When the heat treatment is performed at less than 200° C. and/or forless than 0.5 minute, impurities may not be completely removed and acontact reaction between the ultra-small LED device and the electrodemay not completely occur. When the heat treatment is performed at morethan 1,000° C. and/or for more than 10 minutes, the base substrateand/or the electrode may be deformed or broken and the voltage may notbe properly applied to the ultra-small LED device due to a resistanceincrease. In addition, step (3) is preferably performed again after themetal ohmic layer, which will be described later, is formed.Accordingly, an ultra-small LED electrode assembly that exhibits afurther improved light emitting efficiency may be implemented.

Meanwhile, in the method of manufacturing the ultra-small LED electrodeassembly according to one embodiment of the present invention, afterstep (2), a step of forming a metal ohmic layer at contact portionsbetween the ultra-small LED device and the first mounting electrode andthe second mounting electrode may be further performed. The step offorming the metal ohmic layer is preferably performed after theabove-described step (3).

The reason for forming the metal ohmic layer at the contact portions isfor reducing contact resistance that may occur between the electrode andthe ultra-small LED device when the driving power is applied and furtherimproving the light emitting efficiency. Any metal ohmic layer may beused without limitation as long as it is formed by a conventional methodknown in the art and the present invention is not limited to a specificmethod thereof, and thus a description thereof will be omitted. Also, aknown material may be used as a material of the metal ohmic layer.

The ultra-small LED electrode assembly implemented through theabove-described manufacturing method according to one embodiment of thepresent invention includes the electrode line including the firstmounting electrode 110 and the second mounting electrode 130 which arespaced apart from each other on the same plane and the plurality ofultra-small LED devices 121 and 122 each having one end in contact withthe first mounting electrode and the other end in contact with thesecond mounting electrode, as illustrated in FIG. 1A, and a luminancegain according to the following Equation 2 satisfies 10% or more.

First, a contact type between the ultra-small LED device and each of thefirst mounting electrode and the second mounting electrode will bedescribed. As illustrated in FIG. 5, first mounting electrodes 111 and112 and second mounting electrodes 131 and 132 are formed on the basesubstrate 100 to be spaced apart from each other on the same plane, andthree ultra-small LED devices 123, 124, and 125 are two-dimensionallymounted thereon by being laid down. The first ultra-small LED device 123among the three ultra-small LED devices 123, 124, and 125 is mounted sothat both ends thereof come into contact with upper portions of thefirst mounting electrode 111 and the second mounting electrode 131,respectively. The second ultra-small LED device 124 has one end incontact with an upper portion of the second mounting electrode 131 andthe other end in contact with a side surface of the first mountingelectrode 112. The third ultra-small LED device 125 has both ends incontact with side surfaces of the first mounting electrode 112 and thesecond mounting electrode 132, respectively. As illustrated in FIG. 5,in the electrode assembly according to one embodiment of the presentinvention, there may be various contact types in a single ultra-smallLED electrode assembly, such as the case in which the ultra-small LEDdevice may be inserted into a space between two mounting electrodes andcome into contact therewith, the case in which the ultra-small LEDdevice may be overlaid on two mounting electrodes and come into contacttherewith, and the like. Meanwhile, the present invention is not limitedto the contact types illustrated in FIG. 5, for example, the ultra-smallLED device may be inserted into a space between two mounting electrodesand come into contact therewith by a multilayer being formed in thespace.

In the ultra-small LED devices mounted on the ultra-small LED electrodeassembly according to the present invention, about 60% or more of thetotal number of the mounted ultra-small LED devices are implemented suchthat the same type of semiconductor, for example, a first conductivesemiconductor layer, comes into contact with the same type of electrode,for example, the first mounting electrode, and thus the ultra-small LEDdevices have an improved orientation. Even when an AC is not used asdriving power but a DC is used as the driving power, 60% or more of theultra-small LED devices may emit light and a luminance characteristicthereof may be sufficiently exhibited. Since the DC is used as thedriving power, a circuit configuration is further simplified, and theuse of the DC is advantageous in terms of production efficiency andproduction cost. When less than 60% of the all of the mountedultra-small LED devices exhibit a unidirectional orientation, aluminance exhibited when the DC is used as the driving power issignificantly lower in comparison to a luminance exhibited when an AC isused as the driving power, and thus the ultra-small LED electrodeassembly may not be driven by the DC driving power.

Preferably, the number of the ultra-small LED devices in which the firstconductive semiconductor layer comes into direct or indirect contactwith the first mounting electrode may be 80% or more of the total numberof the mounted ultra-small LED devices. Accordingly, a more improvedluminance characteristic may be exhibited.

In addition, the ultra-small LED electrode assembly according to oneembodiment of the present invention may have 1,000 or more ultra-smallLED devices mounted per unit area (mm²). Accordingly, an excellentluminance characteristic may be exhibited. Meanwhile, an average numberof the ultra-small LED devices mounted per unit area does not refer tothe number of the mounted ultra-small LED devices in a total areaincluding electrode regions in which the ultra-small LED devices may notbe substantially mounted, but refers to the number of the mountedultra-small LED devices obtained by converting the number of the mountedultra-small LED devices on the basis of an area of the electrode line onwhich the ultra-small LED devices may be substantially mounted.

Meanwhile, any ultra-small LED device may be used as the ultra-small LEDdevice provided in the ultra-small LED electrode assembly withoutlimitation as long as it can be generally widely used for a lamp, adisplay, and the like. Preferably, a length of the ultra-small LEDdevice may range from 100 nm to 10 μm, and more preferably, from 500 nmto 5 μm. When the length of the ultra-small LED device is less than 100nm, it is difficult to manufacture a highly efficient LED device. Whenthe length is more than 10 μm, a light emission efficiency of the LEDdevice may be lowered. The ultra-small LED device may have variousshapes such as a cylindrical shape, a rectangular parallelepiped shape,and the like, and preferably, may have a cylindrical shape, but thepresent invention is not limited thereto. In addition, an aspect ratioof the ultra-small LED device may range from 1.2 to 100, may preferablyrange from 1.2 to 50, may more preferably range from 1.5 to 20, and maymost preferably range from 1.5 to 10. When the aspect ratio of theultra-small LED device is less than 1.2, the ultra-small LED device maynot be self-aligned even when power is applied to the electrode line.When the aspect ratio is more than 100, a voltage of power necessary forself-alignment may be lowered. However, it may be difficult tomanufacture a device having an aspect ratio of more than 100 due toprocess limitations when manufacturing the ultra-small LED device by dryetching or the like.

Also, the ultra-small LED device may include the first conductivesemiconductor layer and the second conductive semiconductor layer, andmore preferably, may include the first conductive semiconductor layer,an active layer formed on the first conductive semiconductor layer, thesecond conductive semiconductor layer formed on the active layer, and aninsulating film configured to cover at least an entire outer surface ofan active layer portion of outer surfaces of the device.

In this case, any one of the first conductive semiconductor layer andthe second conductive semiconductor layer may include at least oneN-type semiconductor layer, and the other conductive semiconductor layermay include at least one P-type semiconductor layer. When theultra-small LED device is a blue light emitting device, the N-typesemiconductor layer may be made with a material selected fromsemiconductor materials having a composition formula ofIn_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, and 0≤x+y≤1), for example, anymaterial selected from InAlGaN, GaN, AlGaN, InGaN, AlN, InN, and thelike, and may be doped with a first conductive dopant (e.g., Si, Ge, Sn,etc.). Preferably, a thickness of the N-type semiconductor layer mayrange from 500 nm to 5 μm, but the present invention is not limitedthereto. Since a light emission color of the ultra-small LED is notlimited to the blue color, there is no limitation in using another typeof III-V group semiconductor material as the N-type semiconductor layerwhen the light emission color is different. In addition, the P-typesemiconductor layer may be made with a material selected fromsemiconductor materials having a composition formula ofIn_(x)Al_(y)Ga_(1-x-y)N (0≤x≤1, 0≤y≤1, and 0≤x+y≤1), for example, anymaterial selected from InAlGaN, GaN, AlGaN, InGaN, AlN, InN, and thelike, and may be doped with a second conductive dopant (e.g., Mg).Preferably, a thickness of the P-type semiconductor layer may range from500 nm to 5 μm, but the present invention is not limited thereto. Sincethe light emission color of the ultra-small LED is not limited to theblue color, there is no limitation in using another type of III-V groupsemiconductor material as the P-type semiconductor layer when the lightemission color is different.

The active layer may be interposed between the first conductivesemiconductor layer and the second conductive semiconductor layer. Whenan electric field is applied to the device, light is generated in theactive layer by coupling of electron-hole pairs. The active layer may beformed to have a single or multiple quantum well structure. A claddinglayer doped with a conductive dopant may be formed above and/or belowthe active layer, and the cladding layer doped with the conductivedopant may be implemented as an AlGaN layer or an InAlGaN layer. Inaddition, materials such as AlGaN, AlInGaN, and the like may be used asthe active layer. Preferably, a thickness of the active layer may rangefrom 10 to 200 nm, but the present invention is not limited thereto. Theactive layer may be formed at various positions according to the type ofthe LED. Since the light emission color of the ultra-small LED device isnot limited to the blue color, there is no limitation in using anothertype of III-V group semiconductor material as the active layer when thelight emission color is different.

An electrode layer may be further formed above the first conductivesemiconductor layer and/or below the second conductive semiconductorlayer. When the conductive semiconductor layer further includes theelectrode layer, the contact between the mounting electrode and theultra-small LED device may occur between the electrode layer and themounting electrode and/or between the mounting electrode and both of theelectrode layer and the conductive semiconductor layer. A metal or metaloxide used as an electrode of a conventional LED device may be used asthe electrode layer, and preferably, chromium (Cr), titanium (Ti),aluminum (Al), gold (Au), nickel (Ni), ITO, oxides thereof, or alloysthereof may be used as the electrode, but the present invention is notlimited thereto. Preferably, a thickness of the electrode layer mayrange from 1 to 100 nm, but the present invention is not limitedthereto. When the electrode layer is included therein, there is anadvantage in that the electrode layer and the mounting electrode maycome into contact with each other at a temperature lower than atemperature required in a process of forming the metal ohmic layer at acontact portion between the conductive semiconductor layer and themounting electrode.

The insulating film may include at least an active layer, and an outersurface of the ultra-small LED device may be coated with the insulatingfilm, and, more preferably, at least one of the first conductivesemiconductor layer and the second conductive semiconductor layer may becoated with the insulating film to prevent durability degradation of theultra-small LED device due to damage of an outer surface of thesemiconductor layer. The insulating film serves to prevent an electricalshort-circuit that occurs in the ultra-small LED device when the activelayer included in the ultra-small LED device comes into contact with themounting electrode. In addition, since the insulating film may protectthe outer surface of the ultra-small LED device including the activelayer, surface defects of the active layer may be prevented, and thuslight emission efficiency degradation may be prevented. The insulatingfilm may preferably include at least one material of silicon nitride(Si₃N₄), aluminum oxide (Al₂O₃), hafnium oxide (HfO₂), yttrium oxide(Y₂O₃), and titanium dioxide (TiO2), and more preferably, may include atransparent material which is made of the above components, but thepresent invention is not limited thereto. A transparent insulating filmmay serve as the above insulating film, and, at the same time, and theultra-small LED device may be coated with the insulating film tominimize the reduction of the light emission efficiency which may occur.

Meanwhile, the ultra-small LED electrode assembly according to thepresent invention may include the electrode line including the firstmounting electrode and the second mounting electrode which are spacedapart from each other on the same plane and the plurality of ultra-smallLED devices each having one end in contact with the first mountingelectrode and the other end in contact with the second mountingelectrode. A luminance gain according to the following Equation 2 maysatisfy 1.1 or more, and preferably, may satisfy 1.3 or more.

$\begin{matrix}{{{Luminance}\mspace{14mu}{gain}} = \frac{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{DC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}\mspace{14mu}}{\begin{matrix}{{Luminance}\mspace{14mu}{of}\mspace{14mu}{ultra}\text{-}{small}\mspace{14mu}{LED}\mspace{14mu}{electrode}} \\{{assembly}\mspace{14mu}{driven}\mspace{14mu}{by}\mspace{14mu}{AC}\mspace{14mu}{voltage}\mspace{14mu}\left( {{cd}\text{/}m^{2}} \right)}\end{matrix}\mspace{14mu}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

The above Equation 2 illustrates a ratio of a luminance when DC power isapplied to an ultra-small LED electrode assembly as driving power to aluminance when AC power is applied to the ultra-small LED electrodeassembly as the driving power with respect to the same ultra-small LEDelectrode assembly, and, in this case, a magnitude of a voltage V of theDC power is equal to an effective voltage V_(rms) of AC power having asine waveform. That is, a luminance gain of more than 1 means that evenwhen the ultra-small LED electrode assembly is driven using the DC poweras the driving power, an improved luminance may be exhibited incomparison to when the AC power is used as the driving power. The DCpower may be more efficient than the AC power as the driving power, andthe ultra-small LED electrode assembly may be more suitable for variouselectronic parts and apparatuses using DC power as driving power. Asimple DC driving circuit may be used and may be more advantageous interms of productivity and production cost.

Specifically, an electric field emission spectrum of an ultra-small LEDelectrode assembly (FIG. 2A to 2C) manufactured through a conventionalmanufacturing method, and it can be confirmed that an area of a graphmeasured for each wavelength when a DC voltage of 21.2 V is appliedthereto as driving power is only 0.51 times an area of a graph measuredfor each wavelength when AC power having a sine waveform with a peakvoltage of ±21.2 V and a frequency of 60 Hz is applied thereto as thedriving power, a maximum intensity of light emitted by the ultra-smallLED electrode assembly when DC power is applied thereto as the drivingpower is only about 0.52 times a maximum intensity of light when ACpower is applied thereto as the driving power, and thus a luminance andan intensity of light in a specific wavelength band are significantlylowered.

In comparison to the ultra-small LED electrode assembly manufacturedthrough the conventional manufacturing method, in the ultra-small LEDelectrode assembly (FIG. 2A to 2B) manufactured through one embodimentof the present invention, it can be confirmed that an area of a graphmeasured for each wavelength when a DC voltage of 21.2 V is appliedthereto as driving power is significantly increased to be 1.12 times anarea of a graph measured for each wavelength when AC power having a sinewaveform with a peak voltage of ±21.2 V and a frequency of 60 Hz isapplied thereto as the driving power. In addition, it can be confirmedthat a maximum intensity of light emitted by the ultra-small LEDelectrode assembly when DC power is applied thereto as the driving poweris significantly increased to be about 1.19 times a maximum intensity oflight when AC power is applied thereto as the driving power.

In addition, in an ultra-small LED electrode assembly (FIG. 1A to 1C)manufactured through another embodiment of the present invention, it canbe confirmed that an area of a graph measured for each wavelength when aDC voltage of 21.2 V is applied thereto as driving power issignificantly increased to be 1.43 times an area of a graph measured foreach wavelength when AC power having a sine waveform with a peak voltageof ±21.2 V and a frequency of 60 Hz is applied thereto as the drivingpower. In addition, it can be confirmed that a maximum intensity oflight emitted by the ultra-small LED electrode assembly when DC power isapplied thereto as the driving power is significantly increased to beabout 1.47 times a maximum intensity of light when AC power is appliedthereto as the driving power.

Meanwhile, the present invention includes a lamp including theabove-described ultra-small LED electrode assembly according to thepresent invention. The lamp may further include a support foraccommodating or supporting the ultra-small LED electrode assembly. Anysupport usually used for an LED lamp may be used as the support withoutlimitation, and the lamp may preferably have any one material selectedfrom the group consisting of an organic resin, ceramics, a metal, and aninorganic resin, and the material may be transparent or opaque. Thesupport may have a cup shape or a flat plate shape, but the presentinvention is not limited thereto. The support may be designed to have adifferent shape according to the purpose, and the shape of the supportis not limited in the present invention. When a support has a cup shape,an internal volume of the support may vary in proportion to a size anddensity of the electrode on which the ultra-small LED devices arearranged. Also, the internal volume of the support may vary according toa thickness of the support. The thickness of the support may be the sameat all points of the support or may be different at some point thereof.Since the support may be designed to have a different thicknessaccording to the purpose, the thickness of the support is not limited inthe present invention.

The lamp may further include a phosphor provided inside the support andexcited by light emitted from the ultra-small LED device. For example,when the ultra-small LED device is an ultraviolet (UV) light ultra-smallLED device, a phosphor excited by UV light may preferably be a phosphorhaving any one of blue, yellow, green, amber, and red colors. In thiscase, the lamp may be a single color LED lamp which emits a selectedcolor. Preferably, the phosphor excited by UV light may be a phosphorhaving at least one of blue, yellow, green, amber, and red colors, andmore preferably, may be a mixed phosphor having any one of blue/yellow,blue/green/red, and blue/green/amber/red colors. In this case, thephosphor may irradiate white light. Specifically, since the phosphor maybe selected and used from known phosphors in consideration of a color oflight emitted by the selected ultra-small LED device, a detaileddescription thereof will be omitted in the present invention.

In addition, the present invention may include a backlight unit (BLU)including the ultra-small LED electrode assembly according to thepresent invention.

Specifically, in FIG. 6, a light-receiving display may include a BLU1001, a display panel 2100 positioned on the BLU 1001, and a supportmember 3100 configured to accommodate and support the BLU 1001 and thedisplay panel 2100. In this case, the BLU 1001 may further include alight emitting unit 100,200,900 configured to supply light to thedisplay panel, and a reflective member 1301 which is disposed below thelight emitting unit 100,200,900 and reflects light incident from thelight emitting unit toward the display panel on which an image isdisplayed. The BLU 1001 may further include an optical sheet 1201between the light emitting unit 100,200,900 and the display panel 2100to guide, diffuse, and/or condense the light emitted from the lightemitting unit 100,200,900 into linear polarized light in a specificdirection. The BLU 1001 may further include a heat dissipating member1401 below the reflective member 1301. The ultra-small LED electrodeassembly according to one embodiment of the present invention may beprovided as a light source in the light emitting unit 100,200,900. Sincea known configuration in the display field may be applied to eachconfiguration of the BLU and each configuration of the display, detaileddescriptions thereof will be omitted in the present invention.

Although the present invention will be described in more detail withreference to the following examples, the following examples do not limitthe scope of the present invention, and should be construed asfacilitating understanding of the present invention.

EXAMPLE 1

An electrode line, as illustrated in FIG. 1A, was prepared on an 800 μmthick quartz base substrate. In this case, in the electrode line, awidth of a first mounting electrode was 3 μm, a width of a secondmounting electrode was 3 μm, a distance between the first mountingelectrode and the second mounting electrode adjacent thereto was 2.2 μm,a thickness of each of the electrodes was 0.2 μm, a material of each ofthe first mounting electrode and the second mounting electrode was gold,and an area of a region of the electrode line on which ultra-small LEDdevices were to be mounted was 4.2×10⁷ μm². An insulating partition madeof silicon dioxide and having a height of 0.1 μm from the base substrateto a top thereof was then formed on the base substrate. In this case,the insulating partition was formed on the base substrate to surroundthe region (the area of 4.2×10⁷ μm²) of the electrode line on which theultra-small LED devices were to be mounted.

Then, a solution including the ultra-small LED devices was prepared bymixing 0.7 parts by weight of ultra-small LED device having a structureillustrated in the following Table 1 with respect to 100 parts by weightof acetone.

After 9 μl of the solution was dropped onto the electrode line 8 times,the ultra-small LED devices were self-aligned by applying power of asine wave having 0 to +30 V and a frequency of 950 kHz, as illustratedin FIG. 8, to the mounting electrodes as assembly power.

Heat treatment was then performed to improve contact between theultra-small LED devices and the electrode line. The heat treatment wasperformed at a pressure of 5.0×10⁻¹ torr in a nitrogen atmosphere and ata temperature of 810° C. for 2 minutes, and electroless plating using a0.05 mM gold solution and copper foil was then performed twice at roomtemperature for 10 minutes. The heat treatment was performed again ongold nanoparticles, which were adhered between the electrode line andthe ultra-small LED device by electroless plating being performed underthe same conditions as in the above heat treatment, such that electricalcontact therebetween was improved, and the ultra-small LED electrodeassembly illustrated in the following Table 2 was prepared.

TABLE 1 Length Diameter Material (μm) (μm) First Electrode Layer Chrome0.03 0.5 First Conductive Semiconductor Layer n-GaN 2.14 0.5 ActiveLayer InGaN 0.1 0.5 Second Conductive Semiconductor p-GaN 0.2 0.5 LayerSecond Electrode Layer Chrome 0.03 0.5 Insulating Film Aluminum 0.02 μmoxide Thickness Ultra-small LED Device — 2.5  0.52

EXAMPLES 2 AND 3

Ultra-small LED electrode assemblies in Examples 2 and 3 were preparedin the same manner as in Example 1, but the assembly power applied tothe mounting electrodes was applied to the mounting electrodes as powerof a sine wave having a voltage and cycle illustrated in the followingTable 2, the ultra-small LED devices were self-aligned, and theultra-small LED electrode assemblies illustrated in the following Table2 were prepared.

COMPARATIVE EXAMPLES 1 TO 3

Ultra-small LED electrode assemblies in Comparative Examples 1 to 3 wereprepared in the same manner as in Example 1, but the assembly powerapplied to mounting electrodes was applied to the mounting electrodes aspower of a sine wave having a voltage and cycle illustrated in thefollowing Table 2, the ultra-small LED devices were self-aligned, andthe ultra-small LED electrode assemblies illustrated in the followingTable 2 were prepared.

EXPERIMENTAL EXAMPLE

The following physical properties with respect to the ultra-small LEDelectrode assemblies prepared according to the above examples andcomparative examples were measured, and evaluation results of thephysical properties are illustrated in the following Table 2.

1. Measurement of Total Number of Ultra-Small LED Devices Mounted onUltra-Small LED Electrode Assembly

The ultra-small LED electrode assembly was photographed with an opticalmicroscope to count the number of ultra-small LED devices having bothends coming into contact with two different electrodes.

2. Number and Ratio of Ultra-Small LED Devices Mounted to HaveUnidirectional Orientation

In order to measure the number of ultra-small LED devices which aremounted such that the first conductive semiconductor layer of each ofthe ultra-small LED devices comes into contact with the first mountingelectrode among all of the mounted ultra-small LED devices, theultra-small LED electrode assembly was driven by DC power of +21.2 Vwithout a waveform and a cycle to count the number of ultra-small LEDdevices which emitted light. A ratio of the counted number ofultra-small LED devices which emitted light with respect to all of themounted ultra-small LED devices counted as a result of the abovemeasurement of the physical properties was calculated as a percentage.

3. Visual Evaluation of Light Emitting Intensity

A light emission photograph was taken by primarily applying AC power ofa sine wave having 21.2 V_(rms) and a frequency of 60 Hz to each of theultra-small LED electrode assemblies, and a light emission photographwas taken by secondarily applying AC power of 21.2 V without a waveformand a cycle thereto to drive each of the ultra-small LED electrodeassemblies. As a result of the photographing, the luminescencephotograph of the primary driving according to Example 1 is illustratedin FIG. 1B and the luminescence photograph of the secondary driving isillustrated in FIG. 1C. The luminescence photograph of the primarydriving according to Example 2 is illustrated in FIG. 7A and theluminescence photograph of the secondary driving is illustrated in FIG.7B. In addition, the luminescence photograph of the primary drivingaccording to Comparative Example 1 is illustrated in FIG. 2B and theluminescence photograph of the secondary driving is illustrated in FIG.2C.

Specifically, when looking at the luminescence photographs with thenaked eye, in Examples 1 and 2, it can be confirmed that degrees oflight emission were similar to each other in the primary driving (AC)and the secondary driving (DC) or that light emitted in the secondarydriving was slightly brighter than in the primary driving. However, inComparative Example 1, it can be visually confirmed that light emittedin the primary driving (AC) was much brighter than in the secondarydriving (DC) and a luminance was not very good in the secondary driving(DC).

4. Measurement of Luminance and Peak Intensity

A luminance and a peak intensity were measured with a spectrophotometerby primarily applying AC power of a sine wave having a frequency of 21.2V_(rms) and 60 Hz to each of the ultra-small LED electrode assemblies,and a luminance and a peak intensity were measured with aspectrophotometer by secondarily applying DC power of 21.2V withouthaving a waveform and a cycle thereto to drive each of the ultra-smallLED electrode assemblies. An area value Sum % on an electroluminescencespectrum and an intensity ratio peak % of light having a maximumintensity in each of the examples and comparative examples werecalculated. In this case, the area value and the intensity ratio in thesecondary driving (DC) in each of the examples and comparative examplesare relatively illustrated on the basis of the area value and theintensity ratio in the primary driving (AC).

TABLE 2 Comparative Comparative Comparative Example 1 Example 2 Example3 Example 1 Example 2 Example 3 Ultra-small Application Power 0 V~30 V 0V~13 V +30 V~−10 V −30 V~+30 V 0 V~8 V +30 V~−22 V LED (Assembly Power)950 kHz 950 kHz 950 kHz 950 kHz 950 kHz 950 kHz Electrode forSelf-alignment Assembly Asymmetric Assembly 30 13 20 0 8 8 Voltage (V)in Equation 1 Effective Voltage 18.4 8.0 17.3 21.2 4.9 18.8 of AssemblyPower (V_(rms), V) Total Number of 88,150 59,011 71,185 166,517 20,61590,891 Mounted Ultra-small LED Device Number of Uni- 78,910 36,18957,161 81,005 9,615 44,446 directionally Oriented Ultra-small LEDDevices Uni-directionally 89.5 61.3 80.3 48.6 46.6 48.9 OrientedUltra-small LED Device Ratio (%) Primary Sum % 1.0 1.0 1.0 1.0 1.0 1.0Driving Peak % 1.0 1.0 1.0 1.0 1.0 1.0 (AC) Secondary Sum % 1.43 1.121.31 0.51 0.81 0.97 Driving Peak % 1.47 1.19 1.34 0.52 0.83 0.99 (DC)

As can be seen in the above Table 2, in the ultra-small LED electrodeassembly according to Comparative Example 1, it can be confirmed thatthe intensity of the light emitted when the DC power was used as drivingpower was only 0.51 times the intensity of the light emitted when the ACpower was used as the driving power based on the entire wavelength, andthe peak intensity (peak %) of the light when the DC power was used wasonly 0.52 times the peak intensity (peak %) of the light when the ACpower was used.

However, in Examples 1 and 2, it can be confirmed that a more improvedluminance was exhibited when the DC power was used as the driving powerin comparison to when the AC power was used as driving power. In Example1, it can be confirmed that the luminance was increased to be 1.43 timesthe luminance when the AC power was used as driving power and the peakintensity was increased to be 1.47 times the peak intensity when the ACpower was used as driving power due to the use of the DC driving power.

According to the present invention, since an ultra-small LED device istwo-dimensionally connected to an electrode line, light, which isblocked by an electrode and cannot be extracted, is minimized, theultra-small LED device is connected to an ultra-small electrode withouta defect such as an electrical short-circuit or the like, and thus anexcellent luminance can be exhibited. Also, since a selection limitationof driving power of an ultra-small LED electrode assembly is removed, aluminance characteristic can be sufficiently exhibited even through DCdriving power, and the luminance characteristic can be further improvedthrough the DC driving power. Furthermore, since an intensity of lightcorresponding to a specific wavelength included in an LED itself isfurther improved, an intensity of light of a converted colorsignificantly increases even when the light is converted into light of acolor having another wavelength using the above characteristic.Therefore, the ultra-small LED electrode assembly can be widely used invarious lighting apparatuses and can be applied to electronic appliancesand various parts such as a liquid-crystal display (LCD) BLU and thelike in which an ultra-small LED device is used.

While the present invention has been described with reference to theexemplary embodiments thereof, the spirit of the present invention isnot limited to the embodiments presented in this specification. Thoseskilled in the art, who understands the spirit of the present invention,may easily suggest other embodiments by adding, changing, deleting, orthe like elements within the scope of the same concept, and the otherembodiments may also be within the spirit of the present invention.

What is claimed is:
 1. A LED electrode assembly comprising: a lowerlayer; a first electrode disposed on the lower layer; a second electrodedisposed on the lower layer and spaced apart from the first electrode;and a plurality of LED elements between the first electrode and thesecond electrode, wherein each of the plurality of LED elementscomprises: a first semiconductor; a second semiconductor; and an activelayer between the first semiconductor and the second semiconductor,wherein at least some of the plurality of LED elements is in contactwith the lower layer, and wherein the plurality of LED elementscomprises one or more first LED elements of which a first portion is incontact with the first electrode and is located adjacent to the firstsemiconductor.
 2. The LED electrode assembly of claim 1, wherein anumber of the first LED elements is equal to or more than 60% of a totalnumber of the plurality of LED elements.
 3. The LED electrode assemblyof claim 2, wherein the number of the first LED elements is equal to ormore than 80% of the total number of the plurality of LED elements. 4.The LED electrode assembly of claim 3, further comprising an insulatinglayer on the first electrode and the second electrode, wherein ends ofthe LED elements contact with the first electrode and the secondelectrode through the insulating layer.
 5. The LED electrode assembly ofclaim 1, wherein at least one end portion of the LED elements is on thefirst electrode or the second electrode.
 6. The LED electrode assemblyof claim 1, wherein at least one end portion of the LED elements is incontact with a side surface of the first electrode or the secondelectrode.
 7. The LED electrode assembly of claim 1, wherein theplurality of LED elements comprises one or more second LED elements ofwhich a first portion is in contact with the second electrode.
 8. TheLED electrode assembly of claim 1, wherein each of the LED elements hasa shape of extending in a first direction that is substantially parallelto a second direction in which the first electrode and the secondelectrode are spaced apart from each other.
 9. The LED electrodeassembly of claim 8, wherein a length of the LED elements measured alonga long axis is 100 nm to 10 μm, and wherein an aspect ratio of a longerside to a shorter side of the LED elements is 1.2 to
 100. 10. The LEDelectrode assembly of claim 8, wherein the first semiconductor, theactive layer, and the second semiconductor are sequentially formed inthe first direction.
 11. The LED electrode assembly of claim 10, whereineach of the LED elements further comprises an insulating film coveringan entire outer surface of at least the active layer.
 12. A LEDelectrode assembly comprising: a lower layer; a first electrodeextending in a first direction and disposed on the lower layer; a secondelectrode extending in the first direction and disposed on the lowerlayer, the second electrode being spaced apart from the first electrodein a second direction; a plurality of LED elements, a long axis of whichis aligned in the second direction, between the first electrode and thesecond electrode, wherein each of the LED elements comprises: a firstsemiconductor; a second semiconductor; and an active layer between thefirst semiconductor and the second semiconductor, wherein at least someof the plurality of LED elements is in contact with the lower layer, andwherein the plurality of LED elements comprises one or more first LEDelements of which a portion adjacent to the first semiconductor is incontact with the first electrode.
 13. The LED electrode assembly ofclaim 12, wherein a number of the first LED elements is equal to or morethan 60% of a total number of the plurality of LED elements.
 14. The LEDelectrode assembly of claim 13, wherein the number of the first LEDelements is equal to or more than 80% of the total number of theplurality of LED elements.
 15. The LED electrode assembly of claim 12,wherein the plurality of LED elements comprises one or more second LEDelements of which the portion is in contact with the second electrode.16. The LED electrode assembly of claim 12, wherein the first electrodecomprises a first portion extending in the second direction and a secondportion extending in the first direction, wherein the second electrodecomprises a third portion extending in the second direction and a fourthportion extending in the first direction, and wherein one or more of theLED elements are located between the second portion of the firstelectrode and the fourth portion of the second electrode.
 17. The LEDelectrode assembly of claim 16, wherein the first portion of the firstelectrode and the second portion of the second electrode are spacedapart from each other in the first direction.
 18. The LED electrodeassembly of claim 17, further comprising an insulating layer on thefirst electrode and the second electrode, wherein an end of one or moreof the LED elements is in contact with a second portion of the firstelectrode and the fourth portion of the second electrode through theinsulating layer.
 19. The LED electrode assembly of claim 18, whereineach of the LED elements further comprises an insulating film coveringan entire outer surface of at least the active layer.
 20. The LEDelectrode assembly of claim 19, wherein at least a portion of theinsulating film of the LED elements contacts with the insulating layer.